A Highly Sensitive Resonance Scattering Spectral Assay for Hg2+ Based on the Aptamer-Modified AuRu Nanoparticle-NaClO3-NaI-Cationic Surfactant Catalytic Reaction

Gold ruthenium (AuRu) nanoparticles were modified by single strand DNA (ssDNA) to prepare an aptamer AuRu nanoprobe (AuRussDNA) for Hg²⁺. The nanoprobe reacted with Hg²⁺ to form double-stranded T-Hg²⁺-T mismatches, and the released AuRu nanoparticles aggregated to big particles, which induced an increase in the resonance scattering (RS) signal at 592 nm. The RS signal was linear to the concentration of Hg²⁺ in the range of 0.0067–3.3 nmol L^?1. Using the AuRussDNA in filtration solution as a catalyst, a new catalytic RS assay was proposed for detection of trace Hg²⁺. This method was applied for the determination of Hg²⁺ in real samples.     

Mechanism of mercury detection based on interaction of single-strand DNA and hybridized DNA with gold nanoparticles

Mechanisms of interaction of single-strand DNA and hybridized DNA on gold nanoparticles in the presence of Hg²⁺ was studied in this work. Recently the detection of Hg²⁺ using unmodified gold nanoparticles (AuNPs) combined with DNA is becoming a promising technique with the advantages of simplicity, cost-effectiveness and high sensitivity. However, few studies focused on the interaction of ssDNA and hybridized DNA on AuNPs to date. In the present work, we compared the interactions of different DNA probes on AuNPs using both absorption and fluorescence detection. It was found that there were only small partial dsDNA dissociated from the surface of AuNPs after hybridization in the presence of Hg²⁺. Moreover, we found that the aggregated AuNPs/DNA system tended to be dispersed again with increasing Hg²⁺ concentration up to 250 μM. Based on these results, the mechanisms of mercury detection based on interaction between DNA-conjugated gold nanoparticles were investigated. Positively charged dsDNA could bind to the surface of AuNPs and dominate the electrostatic interactions and consequently aggregation of the AuNPs/DNA system.     

Aptamer-modified AuRe Nanoalloy Probe for Trace Hg2+ Using Resonance Scattering as Detection Technique

The AuRe nanoalloy particles in molar ratio of 9:1 were prepared by sodium borohydride procedure, and modified by single strand DNA (ssDNA) to prepare an aptamer AuRe nanoprobe (AuRessDNA) for Hg²⁺. In the pH 7.0 Na₂HPO₄‐NaH₂PO₄ buffer solution and in the presence of NaCl, Hg²⁺ interacted with AuRessDNA to form double‐stranded T‐Hg²⁺‐T mismatched and release AuRe nanoparticles that aggregate to large AuRe nanoparticles clusters causing the resonance scattering (RS) peak red shifting and the RS intensity enhanced linearly. On those grounds, 0.067–33.3 nmol·L^?1 Hg²⁺ can be detected rapidly by the aptamer‐modified AuRe nanoparticles RS assay, with a detection limit of 0.04 nmol·L^?1 Hg²⁺. If the aggregated AuRe particles were removed by membrane filtration, the excess AuRessDNA in the filtration solution exhibits catalytic effect on the new Te particle reaction between Na₂TeO₄ and SnCl₂. As the concentration of Hg²⁺ increased, the AuRessDNA nanoparticles in the filtrate solution decreased, the RS intensity at 734 nm decreased linearly. The Hg²⁺ concentration (c) in the range of 0.00133–0.267 nmol·L^?1 was linear to the decreased RS intensity (ΔI_734nm), with a regression equation of ΔI= ?786.4c?4.4, a correlation coefficient of 0.9975, and a detection limit of 0.9 pmol·L^?1 Hg²⁺. This method was applied to the detection of Hg²⁺ in water samples, with satisfactory results.     

A Metal–Organic Framework/DNA Hybrid System as a Novel Fluorescent Biosensor for Mercury(II) Ion Detection

Mercury(II) ions have emerged as a widespread environmental hazard in recent decades. Despite different kinds of detection methods reported to sense Hg²⁺, it still remains a challenging task to develop new sensing molecules to replenish the fluorescence‐based apparatus for Hg²⁺ detection. This communication demonstrates a novel fluorescent sensor using UiO‐66‐NH₂ and a T‐rich FAM‐labeled ssDNA as a hybrid system to detect Hg²⁺ sensitively and selectively. To the best of our knowledge, it has rarely been reported that a MOF is utilized as the biosensing platform for Hg²⁺ assay.     

Pt NPs catalyzed chemiluminescence method for Hg2+ detection based on a flow injection system

Establishing a simple and accurate method for Hg²⁺ detection is of great importance for the environment and human health. In this work, platinum nanoparticles (Pt NPs) with different capped agents and morphologies were synthesized. It was found that Pt NPs exhibited peroxidase‐like activity that can catalyze the chemiluminescence (CL) of the luminol system without H₂O₂. The most intensive CL signals were obtained by using PVP‐capped Pt NPs as catalysis. Based on the fact that Hg²⁺ could further enhance the CL intensity in the Pt NPs‐luminol CL system, a Pt NPs‐catalyzed CL method based on a flow injection system is developed for the sensitive analysis of Hg²⁺. When the concentration of Hg²⁺ in the system increases, the CL intensity would together increase, thereby achieving sensitive Hg²⁺ detection. The limit of detection (LOD) was calculated to be 8.6 nM. This developed method provides a simple and rapid approach for the sensitive detection of Hg²⁺ and shows great promise for applications in other complex systems.     

Highly Sensitive Electrochemiluminescence Detection of Mercury(II) Ions Based on DNA‐Linked Luminol‐Au NPs Superstructure

A novel highly sensitive electrochemiluminescence (ECL) detection protocol for mercury(II) ions was developed. Based on the strong and stable thymine? thymine mismatches complexes coordination chemistry, mercury(II) ions can specifically bind to a designed DNA strand, leading to the release of the complimentary DNA strand. The released DNA strand was then captured by magnetic beads modified with specific DNA, and then through the formation of DNA‐linked luminol‐Au nanoparticles (NPs) superstructure, a specific ECL system for mercury(II) ions was developed. Using 3‐aminopropyl‐triethoxysilane as an effective enhancer, the ECL system can detect Hg²⁺ ion within a linear range from 2.0×10^?10 mol L^?1 to 2.0×10^?8 M, with a detection limit as low as 1.05×10^?10 M (3σ). Moreover, this ECL system is highly specific for Hg²⁺, without interference from other commonly coexisted metal ions, and it can be used for the analysis of real samples.     

DNA/Single-Walled Carbon Nanotubes Based Fluorescence Detection of Hg2+

A new, highly selective, and sensitive technique has been developed for the detection of Hg²⁺ using singled-wall carbon nanotubes (SWNTs) and two kinds of oligonucleotides. The fluorescence of the thymine-rich single stranded DNA labeled with dye (the probe ssDNA) was effectively quenched by the SWNTs. In the presence of a target DNA (rich T-T mismatched with probe), the tightness of the DNA wrapping around the SWNTs was loosened. Since binding of Hg²⁺ turned the T-T mismatches to stable T-Hg²⁺-T base pairs, and the binding rate of DNA and the nanotube was lower than that of DNA hybridization, it induced the release of DNA molecules from the SWNTs, and this resulted in a remarkable increase of fluorescence compared to that of the DNA-SWNTs. The assay exhibited a dynamic response range for Hg²⁺ from 4.52 × 10^?8 M to 7.21 × 10^?7 M with a detection limit of 10 nM.     

Label-free aptamer-based colorimetric detection of mercury ions in aqueous media using unmodified gold nanoparticles as colorimetric probe

We report a simple and sensitive aptamer-based colorimetric detection of mercury ions (Hg²⁺) using unmodified gold nanoparticles as colorimetric probe. It is based on the fact that bare gold nanoparticles interact differently with short single-strand DNA and double-stranded DNA. The anti-Hg²⁺ aptamer is rich in thymine (T) and readily forms T–Hg²⁺–T configuration in the presence of Hg²⁺. By measuring color change or adsorption ratio, the bare gold nanoparticles can effectively differentiate the Hg²⁺-induced conformational change of the aptamer in the presence of a given salt with high concentration. The assay shows a linear response toward Hg²⁺ concentration through a five-decade range of 1 × 10⁻⁴ mol L⁻¹ to 1 × 10⁻⁹ mol L⁻¹. Even with the naked eye, we could identify micromolar Hg²⁺ concentrations within minutes. By using the spectrometric method, the detection limit was improved to the nanomolar range (0.6 nM). The assay shows excellent selectivity for Hg²⁺ over other metal cations including K⁺, Ba²⁺, Ni²⁺, Pb²⁺, Cu²⁺, Cd²⁺, Mg²⁺, Ca²⁺, Zn²⁺, Al³⁺, and Fe³⁺. The major advantages of this Hg²⁺ assay are its water-solubility, simplicity, low cost, visual colorimetry, and high sensitivity. This method provides a potentially useful tool for the Hg²⁺ detection.     

Electrochemical aptamer sensor for highly sensitive detection of mercury ion with Au/Pt@carbon nanofiber‐modified electrode

In this paper, an electrochemical aptamer sensor was proposed for the highly sensitive detection of mercury ion (Hg²⁺). Carbon nanofiber (CNF) was prepared by electrospinning and high‐temperature carbonization, which was used for the loading of platinum nanoparticles (PtNPs) by the hydrothermal method. The Pt@CNF nanocomposite was modified on the surface of carbon ionic liquid electrode (CILE) to obtain Pt@CNF/CILE, which was further decorated by gold nanoparticles (AuNPs) through electrodeposition to get Au/Pt@CNF/CILE. Self‐assembling of the thiol‐based aptamer was further realized by the formation of Au‐S bond to get an electrochemical aptamer sensor (Aptamer/Au/Pt@CNF/CILE). Due to the specific binding of aptamer probe to Hg²⁺ with the formation of T‐Hg²⁺‐T structure, a highly sensitive quantitative detection of Hg²⁺ could be achieved by recording the changes of current signal after reacting with Hg²⁺ within the concentration range from 1.0 × 10^?15 mol/L to 1.0 × 10^?6 mol/L and the detection limit of 3.33 × 10^?16 mol/L (3σ). Real water samples were successfully analyzed by this method.     

Highly selective and sensitive visualizable detection of Hg2+ based on anti-aggregation of gold nanoparticles

For the widely used gold nanoparticles (AuNPs)-based colorimetric probes, AuNPs generally change from dispersion to aggregation state accompanying with corresponding color turning from red to blue. Although colorimetric probes based on the anti-aggregation of AuNPs show exceptional selectivity and sensitivity, few examples have been reported in literature. A facile but highly sensitive and selective colorimetric probe based on the anti-aggregation of AuNPs transferred from the deactivation of aggregation agent 4,4′-dipyridyl by Hg²⁺ was developed in this work. This reported probe is suitable for real-time detection of Hg²⁺ in water with a detection limit of 3.0 ppb for Hg²⁺, and exhibits a selectivity toward Hg²⁺ by two orders of magnitude over other metal ions. The dynamic range of this probe can be conveniently tuned by adjusting the amount of 4,4′-dipyridyl used.     

Highly Sensitive Fluorometric Hg2+ Biosensor with a Mercury(II)‐Speci?c Oligonucleotide (MSO) Probe and Water‐Soluble Graphene Oxide (WSGO)

A highly sensitive and selective, "turn‐on" and simple Hg²⁺ biosensor is reported by using water‐soluble graphene oxide (WSGO) and dye‐labeled mercury(II)‐specific oligonucleotide (MSO) probe. The probe is rich of thymine (T) and can readily form the stem‐loop structure which consists of the T‐Hg²⁺‐T configuration. In the absence of Hg²⁺, the probe exists as a random coil conformation which can be readily adsorbed on the surface of WSGO by strong noncovalent binding of bases, as a result, the fluorescence of the dye labeled on the terminus of the MSO is strongly quenched by the efficient electron/energy transfer from the dye to WSGO. Upon addition of Hg²⁺, the formation of the T‐Hg²⁺‐T structure releases the MSO from the surface of WSGO, resulting in a restoration of the fluorescence of dye‐labeled MSO probe. Based on this observation, a highly sensitive and selective Hg²⁺ sensor is developed, which can work with "turn‐on" mode in aqueous solutions at room temperature. By using the fluorometric method, the limit of detection for Hg²⁺ can reach picomolar range (187 pmol·L^?1), and it is demonstrated that the biosensor is highly selective and only minimally perturbed by a wide range of non‐specific metal ions.     

A new BODIPY-based fluorescent “turn-on” probe for highly selective and rapid detection of mercury ions

A new fluorescent sensor based on the BODIPY fluorophore and the carboxyl-thiol metal bonding receptor for Hg²⁺ was designed and synthesized. The sensor is highly selective for Hg²⁺ (about 630-fold fluorescence enhancement) over relevant competing metal ions, sensitive to ppb levels of Hg²⁺ (with detection limit of 5.7?nM), and fast response toward Hg²⁺ (within 30?s) in aqueous solution.     

Highly selective detection of mercury (II) using a G-rich oligonucleotide-based fluorescence quenching method

We provide a highly sensitive and selective assay to detect Hg²⁺ in aqueous solutions using single fluorescence-labeled G-quadruplex at room temperature. The mechanism is that AS1411 converted to G-quadruplex in the presence of potassium ion, and then, by this technique utilizing the high binding capacity of T–Hg²⁺–T makes the fluorescence dye come closer to GGG of AS1411 to causing fluorescence signal quenching by photoinduced electron transfer energy transfer. At physiological pH, the detection limit can be as low as 10 nM, with high selectivity toward Hg²⁺ ions over a lot of metal ions. The linear correlation existed between the fluorescence intensity and the concentration of Hg²⁺ over the range of 0–250 nM (R = 0.9920) in real sample. Accordingly, we expect this G-quadruplex-based sensor will be a potential application for detection of environmentally toxic mercury.     

Biogenic synthesis of silver nanoparticles; study of the effect of physicochemical parameters and application as nanosensor in the colorimetric detection of Hg2+ in water

This research demonstrates the ability of biogenic synthesised silver nanoparticles (AgNPs) to sensitively and selectively detect the presence of mercury (Hg²⁺) in water. To achieve this, the following study investigated the synthesis of AgNPs using plant extract from basil and characterised the synthesised AgNPs using scanning electron microscopy, energy dispersive X-ray spectroscopy, UV-visible spectrophotometry, X-ray diffractometry and Fourier transform infrared spectroscopy. We studied the effect of various factors, such as broth concentration, precursor concentration, temperature, contact time and pH, on the synthesis of the nanoparticles. The synthesised AgNPs were then used in the colorimetric detection of Hg²⁺ in water. The as-prepared AgNPs showed high selectivity to detect Hg²⁺ alone compared to other cations and high sensitivity at different concentration of Hg²⁺. The limit of detection for Hg²⁺ was 6.25 × 10^–8 mol/L (12 µg/L) indicating that these biogenic synthesised AgNPs represent a highly sensitive Hg²⁺ detection tool.     

Sub‐ppt Level Detection of Mercury(II) Based on Anodic Stripping Voltammetry with Prestripping Step at an In Situ Formed Bismuth Film Modified Glassy Carbon Electrode

Sensitive and selective detection of Hg²⁺ in solution is a challenging work. An anodic stripping voltammetry with prestripping step at an in situ formed bismuth film modified glassy carbon electrode was proposed for detection of mercury(II) in solution. This prestripping step was able to decrease the background and improve the signal‐to‐noise ratio and thus enhance the sensitivity. With this method, highly sensitive and selective detection of Hg²⁺ with a ppt‐level detection limit of 0.5 ng L^?1 could be achieved. Moreover, this method provides low interference, rapid and extreme simple and convenience, and hold great promise for in situ Hg²⁺ determination.     

A highly selective nanogold-aptamer catalytic resonance scattering spectral assay for trace Hg using HAuCl4-ascorbic acid as indicator reaction

Single strand DNA (ssDNA) was used to modify nanogold to obtain a nanogold-aptamer resonance scattering (RS) probe (NGssDNA) for Hg²⁺, based on the formation of stable thymine-Hg²⁺-thymine (T-Hg²⁺-T) mismatches and aggregation of the released nanogold particles. After removing the aggregated particles by filtrate membrane, the excess NGssDNA in the filtration solution exhibit catalytic effect on the gold particle reaction between HAuCl₄ and ascorbic acid (AA) that appear as RS peak at 596 nm. When Hg²⁺ concentration increased, the RS intensity at 596 nm decreased. The decreased intensity is linear to Hg²⁺ concentration in the range of 0.00008-0.888 ng/mL Hg²⁺, with detection limit of 0.000034 ng/mL. The nanogold-aptamer catalytic RS assay was applied to determination of Hg²⁺ in water with satisfactory results.     

An Ultrasensitive DNA Sensor for Hg2+ Assay Based on Electrodeposited Au/Carbon Nanofibers-chitosan and Reduced Graphene Oxide

An ultrasensitive electrochemical DNA sensor was designed for Hg²⁺ assay using cooperative signal amplification effect of electrodeposited Au/carbon nanofibers-chitosan (DpAu/CNFs-CS) and reduced graphene oxide (RGO). CNFs-CS was prepared to modify gold electrode (AuE). Then, Au was electrodeposited on CNFs-CS/AuE to form DpAu/CNFs-CS/AuE for the first signal amplification. With TH as signal probe and ssDNA as recognition component, RGO/ssDNA and RGO/TH interaction were used for the second signal amplification. The prepared sensor had wider linear range of 0.0001–460 nM and lower detection limit of 5.7×10⁻⁵ nM, high selectivity, and performed well in Hg²⁺ assay of tap water.     

Microplate electrochemical DNA detection for phosphinothricin acetyltransferase gene sequence with cadmium sulfide nanoparticles

An electrochemical DNA detection method for the phosphinothricin acetyltransferase (PAT) gene sequence from the transgenetic plants was established by using a microplate hybridization assay with cadmium sulfide (CdS) nanoparticles as oligonucleotides label. The experiment included the following procedures. Firstly target PAT ssDNA sequences were immobilized on the polystyrene microplate by physical adsorption. Then CdS nanoparticle labeled oligonucleotide probes were added into the microplate and the hybridization reaction with target ssDNA sequences took place in the microplate. After washing the microplate for three times, certain amounts of HNO₃ were added into the microplate to dissolve the CdS nanoparticles anchored on the hybrids and a solution containing Cd²⁺ ion was obtained. At last differential pulse anodic stripping voltammetry (DPASV) was used for the sensitive detection of released Cd²⁺ ion. Based on this principle a sensitive electrochemical method for the PAT gene sequences detection was established. The voltammetric currents of Cd²⁺ were in linear range with the target ssDNA concentration from 5.0 × 10^− 13 to 1.0 × 10^− 10 mol/L and the detection limit was estimated to be 8.9 × 10^− 14 mol/L (3σ). The proposed method showed a good promise for the sensitive detection of specific gene sequences with good selectivity for the discrimination of the mismatched sequences.     

Ultrasensitive mercury(II) ion detection by europium(III)-doped cadmium sulfide composite nanoparticles

With the biomolecule glutathione (GSH) as a capping ligand, Eu³⁺-doped cadmium sulfide composite nanoparticles were successfully synthesized through a straightforward one-pot process. An efficient fluorescence energy transfer system with CdS nanoparticles as energy donor and Eu³⁺ ions as energy accepter was developed. As a result of specific interaction, the fluorescence intensity of Eu³⁺-doped CdS nanoparticles is obviously reduced in the presence of Hg²⁺. Moreover, the long fluorescent lifetime and large Stoke's shift of europium complex permit sensitive fluorescence detection. Under the optimal conditions, the fluorescence intensity of Eu³⁺ at 614 nm decreased linearly with the concentration of Hg²⁺ ranging from 10 nmol L⁻¹ to 1500 nmol L⁻¹, the limit of detection for Hg²⁺ was 0.25 nmol L⁻¹. In addition to high stability and reproducibility, the composite nanoparticles show a unique selectivity towards Hg²⁺ ion with respect to common coexisting cations. Moreover, the developed method was applied to the detection of trace Hg²⁺ in aqueous solutions. The probable mechanism of reaction between Eu³⁺-doped CdS composite nanoparticles and Hg²⁺ was also discussed.     

Fluorescent Gold Clusters as Logic Gates for the Detection of Different Metal Ions

Metal cations can be selectively detected by restoring and quenching the fluorescent intensity of an “ON–OFF” gold nanocluster (Au NC ) sensor. The fluorescent intensity of Au NCs with metal cations can be restored by chelating with ethylenediaminetetraacetic acid except for Hg²⁺ ions. A highly selective detection of Hg²⁺ ion is also achieved under the coexistence of Fe³⁺ or Cr³⁺ ions. This assay was applied successfully for detecting Hg²⁺ in a water sample. The dynamic range of the system was 1 ppm to 25 ppb, and the limit of detection was 25 ppb.